Somebody should stuff Terry K down a storm sewer...
That's just plain ignorant. But with a "plastic ball valve" for a
seacock, it's just a matter of time till his boat sinks, and then it
will be fuel and oil that he'll be fouling the waterways with, not just
sewage...sheesh! A marelon valve is ok as a seacock, but judging by his
statements, I suspect Terry is more of a PVC from Home Depot kind of
guy...
And if you skip the vented loop with your system below the water
line, You stand a good chance of sinking your boat as well, Roger. Do
yourself a favor and check out this link to see how a system should be
constructed, instead of over/under engineering it in your head. This
tutorial will answer all your questions, and it has drawings of all
common configurations....
http://www.westmarine.com/webapp/wcs...tionsystem.htm

....And if you see some dipstick dumping his boat OR RV in a sewer,
call 911 and turn the idiot in..