Shower Drain Issues

[Lance Jones]

The swap out of the check valve is complete!!! Woo-hoo, little - if any back wash.

[Ron Hill]

Lance : I hope you put a filter/strainer before that one way valve or it WILL get clogged.  A thought

[Ken Heyman]

While on the subject, I have the standard setup i.e. shower drain plumbed to the head thru hull. What is interesting is that when I open that sea cock and pump the shower basin , the toilet fills up(as opposed to the water being discharged into the sea)  with the water from the shower basin. I could understand this happening with the thru hull closed but can't figure why the shower water isn't discharged into the "sea" when the thru hull is open.---it's seeking the course of least resistance but why is that the toilet? BTW I did search for the answer but couldn't find this oddity addressed specifically. I know that none of the lines are clogged since I can get water to the head from the sea and can pump water from the shower to the head thru the hoses.--a partial clog maybe?

Ken

[Mike and Joanne Stimmler]

Ken,
Is the switch position on the head in the dry bowl position or the flush position? I should NOT happen if it's in the dry bowl position. I know my head will continue to fill after flushing if I don't change to dry bowl or close the through hull sea cock.

Mike

[Ron Hill]

Ken : As Mike pointed out the "path of least resistance" (if the toilet valve is on wet bowel) is in to the head bowel !! 
You might also want to check that double fitting and the head/drain thru hull for any kind of obstruction. 

[Ken Heyman]

thanks Ron and Mike,

I think you may have the answer. The switch is inoperative. It allows water into the bowl regardless of position if the sea cock is open. I'll replace that switch check for a partial clog and enjoy future flushing into the sea---- thanks guys!

Ken