I'd agree with the once money has exchanged hands to wet wipe going in the bin. I tend to shower before leaving my place and then again when I get home. I can usually go 30min without a drink, a toilet break or a meaningful conversation.
Seems reasonable to me. But I've mostly tended to 'arrange' 30min outcalls to mean 30mins of shagging, sucking, nibbling.
Me: "Would you like a drink?"
(allows her to choose/pour herself from a selection if she looks physically brisk)
Me: "Shall I bring the drinks thru to the bedroom"
(I usually wait only for the nod of assent as I'm carrying them through)
Me, after 30mins of shagging, sucking, nibbling: "Can I top your drink up?"
It mostly hasn't been touched, unless to get some quick liquid after shag-end.
I am not overly generous with drinks, but the cost is negligible. However
a) I have given her a warm welcome and established the ambience I want
b) I've put her at ease by allowing her to be in control and not worrying about the possibility of anything being spiked
c) I've used the drink as a prop to move things along through to the bedroom very quickly and without breaking the atmosphere
d) If she wants to chat in her own time at the end of the punt I've made it clear she's welcome to drink while we do so.
In other words I feel that getting what I want in a courteous, responsible and cost-efficient manner to be my job. Why leave it to chance???
I think this is basically what the experienced punter does. The experienced prossie usually picks up on the fact that he is not threatening or manipulative but fair, respectful and pleasant company, and on that basis lets him run the show. (This advice might not always work so well in the large English cities unless you are able to go through middle men who can vouch for prossie and punter.)