Plumbing question.

[Frank P]

New to fifth wheel. Just took possession of our 2019 Grand Design Momentum 395M. Trying to figure out how to dump grey and black water tanks. I dumped using the two dump handles at the front of the rig ok, but monitor shows one of the black water tanks still over half full. Also not sure what the dump outlet, located aft of the the left side wheels, is for.

[Cate&Rob]

Hi Frank,

Welcome to this forum!

The usual dumping practice is to dump the black tank first. Then, dump the grey tank second, to flush any remaining black tank contents out of the pipes and hoses. The level gauges are notorious for being inaccurate. Particularly the black tank. If a small piece of anything is hung up on the sensor probe it will give an inaccurate reading.

The gate valve behind the left rear tire is likely the fresh water tank drain. Particularly if it is white plastic rather than black. If it is black and you have a second washroom in that area, it would be a drain for that second black tank.

Rob

[Frank P]

Thanks Cate & Rob. The gate valve behind the tire is white and it did start to drain the fresh water. Just behind that gate valve is another opening to attach sewer hose to. Do you know what that’s for?

[Cate&Rob]

Thanks Cate & Rob. The gate valve behind the tire is white and it did start to drain the fresh water. Just behind that gate valve is another opening to attach sewer hose to. Do you know what that’s for?

Hi Frank,

Do you have a washroom in the "garage" part of your Momentum ? (more-or-less directly above this aft sewer hose connection) If so, this second connection is probably for the single combined black and grey tank for that washroom.

Rob

[Frank P]

There is a small bathroom above the sewer outlet.