This question was posed to me today and I realized there is nothing in my writings that address this question, one that does come up. You don’t want a lot to build up and cake in there over years of use on any horn but especially on a triple or descant that has a valve in the leadpipe.
Many if not most models of descant and triple horns have a valve in the leadpipe. You should not snake this type of leadpipe as you would the leadpipe of a standard instrument. Instead I suggest using a Q-tip carefully up at the receiver to clean out the junk there (try not to push crud down into the horn in the process) then blow water through the leadpipe to remove the rest of the crud. If you do this often at all things will stay pretty clean.