Howard, you really need to replace the valve
'Cuz when the dry/flush valve fails, sooner or later it's also gonna hang up...you won't be able to flush the toilet. It's not an expensive part.And because it's all too easy--especially since it's not ingrained in your brain as a habit yet--to forget to close the seacock, I strongly recommend that you also install vented loop in the head intake. It goes between the pump and the bowl, and should be at least a foot above the waterline at any angle of heel. That will allow you to leave the seacock open when you're in the slip or at anchor, but not when you're underway. Although a vented loop breaks a siphon, it can't stop an effect known as "ram water" (water forced up the hose by the pressure of the water against the hull by the motion of the boat going through it). It only takes about 20 minutes on the "right" tack at hull speed for that to overflow a toilet bowl...I've been aboard more than one boat when it happened. It's not likely to sink the boat, but it can certainly make a mess. And btw...while you have to the pump apart to replace the dry/flush valve, take advantage of the opportunity to give the pump a good lube job...slather the inside of it liberally with SuperLube--the same thick teflon grease used by toilet mfrs. Unlike anything you pour down the toilet, it lasts at least a year. A tube of it is about $2, available from any decent boat store.