Peggy, The West Marine 2001 Master Catalog, page 526, shows several plumbing alternatives for the sanitary system. I know you can't speak for West Marine, but can you explain the following? One set up shows the discharge at the toilet connected to a Y-valve. One side of the Y-valve goes to a lectra/san (or holding tank), and the other side of the y-valve goes to a "T" at the overboard discharge seacock. The other side of the "T" that connects to the seacock loops back to the lectra/san discharge (or holding tank discharge through a manual waste discharge pump/deck pumpout). Depending on the position of the y-valve at the toilet, effluent is dischaged diretly to the overboard seacock, or through the lectra/san (or holding tank - to be pumped out at the deck, or overboard with the manual waste pump). My question is: When dischaging the toilet directly overboard, what stops the effluent from backing up into the lectra/san (or holding tank manual waste pump) when it reaches the "T" at the seacock (or visa-versa: i.e., backing up into the toilet discharge line down stream of the y-valve when dischaging the lectra/san)? Even with fluid in the lectra/san discharge line (or holding tank discharge line), it seems to me that solid waste could be packed into the "T" on the lectra/san (or holding tank) discharge line side. Shouldn't there also be a y-valve connected directly to the seacock, one side attached downstream of the y-valve at the toilet, the other side attached to the lectra/san (holding tank) discharge. This would positively prevent the backup of effluent into either line no matter what the operation. Of course, with this set up, it would be necessary to set two y-valves every time you change discharge configuration. But isn't this the only way it will work? Thanks you for your help. Kim Efishoff