But there is a remote possibility that the seal dried out while it was out of use. So,
you can use cooking oil, but I prefer to use Murphy's Wood (Oil) Soap

I am reminded of an advertisement I saw on TV where these two cleaning
ladies are sprucing up the wooden pews in a church, using, yes you guessed
it, Murphy's Wood (Oil) Soap.

And here you are suggesting that it be used to refurbish the black and gray
water valves. I think it could be described in a different way, but hey,
those cleaning ladies are in a church and I should have some respect, eh?

Sincerely,

Peter K. Kaiser
Thornhill, Ontario
http://members.home.com/pkaiser