Galley sink drain

[GTL48]

2016 FC30. When draining full galley sink it comes up in the shower floor drain. Doesn't happen with lav sink and shower drains ok with normal use. Brad at Airstream service advises this is normal and to try draining sink slowly. Never had this problem with our 2005 Classic 34. Anybody else have this happening?

[xrvr]

This has been covered in the past, pretty much normal. Might be a fix, though.

[dkottum]

Hasn't happened to us but I think it could, that shower drain is very low. Only solution I would do is to drain the sink a little slower so the water doesn't back up in the drain pipe. The lav sink may drain into the black tank, rather than the gray tank, through a different drain line, ours does.

[tjdonahoe]

My 2013 31' classic will do the same thing, the only fix is to change the drain lines in the closet, so now we drain the sinks slower.....

[PaulnGina]

How many thousands of dollars do you have to spend to get a sink that will drain without backing up somewhere else?
Having been in a service business for 35 years, "That's normal" is a pretty poor answer.