water heater drain mod

I have an Atwood water heater, so Rheem instructions are immaterial.

Well then do what you want.

No matter the manufacturer the t&p valve needs to be tested periodically.

See page 5 of the Atwood instructions. It Says to open the t&p valve to allow air in to help drain the tank. It also says to operate the t&p valve once a year.

Atwood instructions

msmith1.wa wrote:
For those that don't think you should open the t&p valve. The instructions linked below from Rheem recommend doing it at least yearly.

T&P valve instructions

I have an Atwood water heater, so Rheem instructions are immaterial.

For those that don't think you should open the t&p valve. The instructions linked below from Rheem recommend doing it at least yearly.

T&P valve instructions

Again... I don't think popping the valve 10-15 times in its life will damage it. If you are afraid it will, just don't park on that side of my camper or park uphill. The over-analyzation on this board can get a little thick at times...

But whatever, you can accomplish the same thing by going inside and opening the faucet. Its much easier than rigging up some drain plug and shutoff valve that may or may not cause galvanic reactions with your aluminum tank.

It is a relief valve not a vacuum breaker. The valve is designed to hold a set temperature or pressure. The spring handles the pressure part. It is designed to hold the seat down until the pressure overcomes the design of the spring, then the seat lifts momentarily so the pressure is relieved then it reseats. When you operate the lever on the valve to use it as a vacuum breaker you are over compressing the spring and holding overcompressed until the tank completely drains, unless you leave the lever set and forget to flip it back. Continued cycles of over compressing the spring nd holding it compressed will cause the spring to get weaker and not allow the valve seat properly. So, operating the lever on the valve unnecessarily can cause the spring to weaken and the valve to fail.

philh wrote:
That won't completely empty the WH. You can also flush out the WH when you pull the plug

I haven't measured how much water comes out of the hot line, but it is quite a bit. I might not drain every last drop, but I would guess that I drain the vast majority of the water. Certainly I've drained enough to allow for expansion if the last bit freezes. On my water heater, the fill line is quite close to the bottom of the tank and the agitation of the water as it leaves likely stirs up any possible sediment that is left in the bottom. I just don't see any benefit to spending money and rigging up a series of hoses and valves and do-dads to drain the same water from roughly the same low point. But hey, you do you.

coolmom42 wrote:
I've been told that the water heater will not drain through the low point drains. Apparently there is a check valve on the incoming cold line. There must be some reason it won't drain through the low point drain on the hot water line, although that doesn't make a lot of sense to me.

Perhaps on some campers, but not any that I have seen. Its very easy to tell. Next time you break from a camping trip, open both low point drains and break the vacuum by opening up a faucet. Your cold water will drain quickly. If you don't have a check valve, your hot water will drain for a much longer time and come out steaming hot.

coolmom42 wrote:
I opened the drain, and a hot water faucet, with the water pump turned off. WH drained quickly and down to the level of the drain.

It's not clear to me why you would need to open the pop-off to relieve pressure. There won't be pressure on the system unless the pump or city water connection is active, and it's relieved by opening a faucet.

Correct, opening the hot water at the faucet or the valve will break the vacuum. I usually open at the faucet throughout the year, but once a year when I winterize I do it at the pressure relief valve. Its faster to drain, and usually its getting chilly outside when I winterize and I don't want to stand aroundl onger waiting. I don't think that popping the valve 10-15 times in its life will damage it. If anything, it would jar loose and sediment that has built up around it.

I opened the drain, and a hot water faucet, with the water pump turned off. WH drained quickly and down to the level of the drain.

It's not clear to me why you would need to open the pop-off to relieve pressure. There won't be pressure on the system unless the pump or city water connection is active, and it's relieved by opening a faucet.

coolmom42 wrote:


I've been told that the water heater will not drain through the low point drains. Apparently there is a check valve on the incoming cold line. There must be some reason it won't drain through the low point drain on the hot water line, although that doesn't make a lot of sense to me.

It won't drain through the hot line because the intake for the hot line is set high up in the tank. (Hot water rises.) As soon as the tank water level falls below that, it quits siphoning. Draining through the cold line is better, but you don't know just how low the water inlet is inside the tank. Once the water level falls below that intake, it quits siphoning. Another thing is you have to open the pop-off valve to vent the tank so it can drain. That is probably the reason you were told it can't be drained through the low point drains. It is not good for the pop-off valve to be opened like that on a regular basis. It is not an on/off valve. It can lead to premature failure of the pop-off valve.

My Atwood WH has a brass Watts 3/4 100 XL T&P with dope on the threads. I put the brass valve in the drain with tape. My 13 year old T&P started dripping and I’ll be looking at the threads very closely when I replace it next week. Craig