We have a Jayco Baja. It came with a Thetford cassette which works great. However, my husband, who is in charge of the Thetford, is wondering why the hooch wasn't plumbed with a black water tank? It has a grey water tank which takes in the shower water only. (We rarely shower in the Baja and so it is empty 95% of the time.) So, portal experts....is there some reason why the black water couldn't be diverted to the grey water tank which, ostensibly, would hold more than our little cassette?