Replacement Dometic 300 series toilet water valve

Guess I didn't look at the dates..

Forgot about folks digging old threads out of the crypt..

Glad you got it worked out!

Gdetrailer wrote:

Now days, you do have to use your imagination and rummage through nearly every store you can find in order to get every fitting you need.. Sure miss the little hardware stores on the corner that had every single obscure plumbing item..

That's for sure.

I forget the fitting I eventually found (this thread is 6+ months old). It was a gray elbow and had internal thread that fit onto the valve thread and with a heat gun I managed to get the OEM Winnebago tubing around the lightly barbed fitting.

It was still a no-go until I had my euraka moment of fitting it to the valve assembly before attaching that to the toilet.

I tied the brass elbow you pictured but it was too small for the OEM Winnebago hose/pipe/tubing.

Sharkebite and SS pipe was going to be my last resort as I would have had to pull out some of the bulkhead and it would have looked like sh*t.

mcewena wrote:

Gdetrailer wrote:

mcewena wrote:
I've got to take part of the blame for this one. I was assured by several people that the dometic 300 was a plug and play replacement for my unit but the supply line faces the rear as opposed to the side like the old one and even with the shallowest elbow I could find it still tweaks the valve assembly on a rear bulkhead when in use. I thought I shaved enough off the bulkhead but apparently not. More exacto knife required.

Change the stiff PEX supply line to flexible plastic line with braided stainless steel..

Thanks but no. The problem is the dometic supply points directly at the bulkhead wall and there isn't room to put a standard elbow on it nor the ss line without it rubbing against the wall and constant pressure being applied to the valve assembly which, over time, causes it to leak. I solved it by attaching an elbow directly to the supply line and screwing that elbow into the valve assembly BEFORE snapping the assembly into to the toilet.

Sounds like you need a "short radius" elbow or something like a "street Ell" to connect the valve to the supply line..

If you had a PEX crimper, you could change the fitting on the PEX with a 90 degree swivel which has a very tight and short radius..



Another option is a "TEE", cap off one side and connect line to the other..looks like this..



Now days, you do have to use your imagination and rummage through nearly every store you can find in order to get every fitting you need.. Sure miss the little hardware stores on the corner that had every single obscure plumbing item..

I still stand by the suggestion of using the flexible braided line, no matter how much you play with bending PEX, it will want to go back the way it was .. Flexible lines remove all of the pressure that PEX would create on the water valve..

But you may get better ideas if you were to post a photo and a couple of the dimensions for clarity.. We are only able to guess as to the issue you have and the space you have to work with without a photo..

I have changed not only the toilet feed to flex lines but the bathroom sink and kitchen sink also..

On edit..

Found a 1/2" to 1/2" street elbow..



Found HERE

Which has a very sharp 90 degree turn that would allow some space over normal 90 elbows..

You can use the measurement in the photo above to get an idea on how tight it is..

Was looking to see if there was any flexible braided hoses with 90 degree turn on them but looks like not much other than hose bib ones for washing machines..

Like these..



Sure would be the cats meow if you could find that in 1/2" pipe thread..

Gdetrailer wrote:

mcewena wrote:
I've got to take part of the blame for this one. I was assured by several people that the dometic 300 was a plug and play replacement for my unit but the supply line faces the rear as opposed to the side like the old one and even with the shallowest elbow I could find it still tweaks the valve assembly on a rear bulkhead when in use. I thought I shaved enough off the bulkhead but apparently not. More exacto knife required.

Change the stiff PEX supply line to flexible plastic line with braided stainless steel..

Thanks but no. The problem is the dometic supply points directly at the bulkhead wall and there isn't room to put a standard elbow on it nor the ss line without it rubbing against the wall and constant pressure being applied to the valve assembly which, over time, causes it to leak. I solved it by attaching an elbow directly to the supply line and screwing that elbow into the valve assembly BEFORE snapping the assembly into to the toilet.

Somewhere about here I may have a spare OEM if I have not tossed it. (I think I tossed it)
But they are easy to replace. That's the point of this post.

mcewena wrote:
I've got to take part of the blame for this one. I was assured by several people that the dometic 300 was a plug and play replacement for my unit but the supply line faces the rear as opposed to the side like the old one and even with the shallowest elbow I could find it still tweaks the valve assembly on a rear bulkhead when in use. I thought I shaved enough off the bulkhead but apparently not. More exacto knife required.

Change the stiff PEX supply line to flexible plastic line with braided stainless steel..

Like this..


You will need 1/2" to 1/2" pipe thread on the ends..



Cut off the PEX add a "Shark Bite" threaded connector to the PEX and you are done.

Very simple and easy upgrade to handle those potential leaks caused by stiff PEX.

And yes, it IS possible to damage or break the water valve if there is too much mechanical pressure exerted from the stiff PEX.

You can lightly heat PEX with a heat gun to soften it so it will bend easier and when it cools it should retain most of the bend.. Takes a few tries to learn how much heat and it is easy to over do the heat which is why a used the flexible lines with the stainless braid.

As for the fill valve, yeah, the OEM is cheaply made, but so is the cheap knock offs..

If the damage was self inflicted from the PEX line I would suggest going with another OEM valve. The cheaper knockoffs may be even less quality and personally having one of these breaking off or flooding the trailer is not a good idea..

Deleted---posted in error

I've got to take part of the blame for this one. I was assured by several people that the dometic 300 was a plug and play replacement for my unit but the supply line faces the rear as opposed to the side like the old one and even with the shallowest elbow I could find it still tweaks the valve assembly on a rear bulkhead when in use. I thought I shaved enough off the bulkhead but apparently not. More exacto knife required.

We bought a new Mallard in '88, A new Itasca in '01, and another Itasca in '15. The 2015 Itasca toilet both the seal and fill valve have gone bad, the other 2 MH toilets never went bad. There are no parts available for the leaking toilet.

I am not of any help for your question but wanted to say I feel your pain in that I had the same problem and almost flooded the entire rv when the valve wouldn't shutoff and continued to fill the toilet bowl. Dometic replaced mine under warranty and I replaced it myself. After doing this I cut the old one apart to see what made it tick. Well what I saw made me wonder how any company would dare provide such **** to the public. I'd almost think any other source for this valve must be an improvement.