Posted: Sun Jul 15, 2018 12:38pm
I can't comment on the olive oil advice although my guess is it might actually attract them, dunno.
However - before you leave next time, run plenty cold water through all the taps. Then pour a fair bit of bleach into the plug holes. Leave for 10 minutes and then flush through with more cold water. Then put plugs into all the sinks. If your shower is above bath put that plug in too. If it's a stand alone shower cover the drain. See if that stops it.
But if you don't already have one find a food particle strainer for your kitchen sink and use it when you empty the sink as it will prevent any nice snacks remaining in the pipes while you're not there.
Steve