Open or closed

It's been a long time since I've drained my black tank when it was full. When camping, I dump it about every other day. Yea, it's not full. But, with a Flush King attached and both black and grey water coming out the same port, I always back-flush the grey into the black after initially dumping the black. It always works. Look in the hole of the toilet with a flash light and the bottom of the tank is clean. I can see the pop-rivits right under the hole in the bottom.

So... you really do not have to wait till its full to dump... but you do need to flush it out, with either a built in flusher sprayer, back flushing, filling the tank via the toilet with water, or using a flush king system to rinse the tank. That back-flushing really pulls out more stuff, even when the tank (is) full.

To answer the OP's question. Leave the tanks closed until ready to dump. Do not leave them open. Water will drain out leaving solids behind ... even with your grey and kitchen water water.

You can drain any time, but keep it closed until you do. And if you drain before the tank is full, rinse or backwash the black. You'll never have problems if you always back-flush.

Black and GREY dump valves closed until time to dump

Black is obvious due to poop......don't want to have the liquids drain away and leave poop behind

BUT GREY can have same issues.
Food debris, grease/oil, sloughed skin, body oils etc can be left behind if drain left open.
That is reason grey stinks as bad (worst) then black tank

Both drain valves closed until tank full for that WHOOSH effect when dumping.

I have read on here about some campers that have left their grey tanks open and gotten flies and/or bugs in their tank. I never experienced this but I leave mine closed until I am ready to dump.

DutchmenSport wrote:
It's been a long time since I've drained my black tank when it was full. When camping, I dump it about every other day. Yea, it's not full. But, with a Flush King .....

Just wondering why you do this.

Bottom line...
Always have liquids in the black tank.
Done for the weekend, heading home. Dump 2-5 gals of soapy water in the tank and let it slosh around for the ride home, leave it there till your next dump.

Valkyriebush wrote:
Blk closed, grey open. Close grey a day before dumping blk. As per previous comment.

X2

We are set up as seasonal through the summer months. I keep black closed and grey open. My trailer has a rinser for the black tank that I use when dumping. My grey is open 5-6 months per year, never had any issues.

Here is the routine I have developed over the last winters snowbirding.

1. Get a clear sight adapter and put it between the trailer and the sewer hose.
2. I leave the black tank closed for a week at a time. Grey tanks open.
3. I form a pee trap in the sewer hose with a couple boards, one 2x and a 4x4.
4. To dump and flush, I remove the pee trap boards.
5. Close the grey water tanks.
6. Open the black water tank and turn on the hose to the built in flush system.
7. Watch the sight tube until I am down to just hose water coming out.
8. Go inside and do two full bowl super flushes. "Bomb the Pile!" Note: Full bowl means filling the bowl to the bottom of the upper rim.
9. Go back outside and view discharge.
10. Close the black water tank and run the flush water in for four(4) minutes. Do not let anyone distract you at this point.
11. Open and drain and repeat 10 again.
12. Flush a bit and verify that you have nice clear water coming out of the tank. If not go back to step 8 and start again.
13. When you have nice clear discharge, put the pee trap boards back the sewer line and fill the pee trap.
14. Close the black water tank and add about a minute worth of water to the tank with the flush hose.
15. Secure the flush hose. I have a little inline valve adapter at the side of the trailer and the other end get turned off.
16. Open the grey water tanks and go add your chemical to the tank.

I have had the burping a couple of times, however the super flushes seem to have fixed that issue.

Having piles in not good!!

Jayco-noslide wrote:
I leave both valves closed and don't even have the sewer hose connected. Then when the tanks are near full, I hook up and dump. My theory is that it's better to get all that water flow at once to flush out the tanks and I don't have to worry about the sewer hose sealing to the one in the ground, etc.

This is what I do. No need to hook up the stinky slinky until Im ready for it.

Mike

We only have FHU's at about half the places we visit. When at a FHU site, our hose is connected and the galley (kitchen sink) tank valve is open. The tank for the shower and bathroom sink, and the black tank, is closed until ready to dump.

The only thing that dictates this decision for us is that the sewer connection and valve for the galley tank is under the slide, so not very easily accessed when the slide is out.