Right, you know where your dogs lips have been.
I know where my ‘male’ dogs tongue has been and I don’t let him lick my mouth!
If you really don’t want to pack mask & snorkel (or pay the price for something you will use one a year) go to your local dive shop and buy a new mouth piece. The dive operator will be happy to put it on one of their snorkels if you tell them you are ‘donating’ it to them. I suggest you mark it in a way that you know that you will get it each day when you go with them.