I have a 2016 Sundancer 340. I've...

[ernie2]

I have a 2016 Sundancer 340.   I've got air bubbles in the fresh water system and think I've chased it down to the freshwater tank.  I've replaced the fresh water pump and even shut off the manifold to see if it would pressurize the 2 feet of pex between the pump and the manifold.   I can see bubbles in the line going from the water pump to the tank. I've also noticed that the problem goes away with the tank is full and becomes worse as it empties.  My current theory is that there's a hole or crack in the pickup tube.  Does anyone know how to replace it?  I was able to access it and I believe is the middle 90 degree piece (with a seven on it) that needs to be replaced.  I *think* it's threaded into the tank but want to be sure before I start putting pressure on it.  

Does anyone know what this part is and how I get a replacement?  Can it be removed by just unscrewing it from the tank?  Also, there's a clear silicon, does that need to be re-applied?  What product is it?  

Thanks!!!

[wingless]

The symptoms and analysis appear correct and appropriate.

The image looks to have a sealant where all four fittings are attached to the tank.

My speculation is the tank manufacturer seals those fittings to the tank during the manufacturing process, prior to welding the final panels to the tank, when both the interior and exterior may be accessed.

If all that is correct and if there is an internal problem then correcting that problem would require either tank replacement, or cutting the tank and welding the cut.

[ernie2]

Thanks wingless for the review. Just confirming, does all that still apply if the tank is plastic?

I guess if the answer is a tank replacement, I've got nothing to lose spinning the base of the fitting and crossing my fingers it's threaded

[wingless]

YW

Yes, plastic welding is common.

IMO, I don't see a benefit w/ loosening the sealed fitting for the pickup tube and also see a risk for problems w/ touching that nut.

[ernie2]

ok... so now to find a replacement. Any idea if these tanks are standard sizes or do i need to find someone local to build me one?

[wingless]

Probably custom.

Why not see if a plastic tank welding manufacturer can open your tank, swap the pickup tube and weld it shut?

[ernie2]

i'll have to call around tomorrow when shops are open. Also found a guy on the clubsearay forum that was having an almost identical issue - http://www.clubsearay.com/index.php?threads/head-vacu-flush-wont-flush-and-fresh-water-systems-spurts-water.104448/page-3

[wingless]

The steps in that link appear appropriate and look to be a good starting point.

[ernie2]

I just wanted to close the loop on this in case someone finds this thread down the road. FINALLY got a plumber out to see what's going on. Turns out the pick-up tube is threaded after-all. Looks like the white elbow was cracked. I feel a little silly in that I could have easily fixed that.... but was worried I'd try to spin something that wasn't supposed to spin.

He's also replacing the toilet drain to the vaccu-flush, that's a job I didn't want to mess with so it was worth him coming out.

Hope this helps someone down the road with a similar issue