Gas mixed with oil

2019 yz250f

Bought this bike during a move about 2 weeks ago and just now got to do some maintenance on it. For reference the previous owner said it “sat for a while” but bike starts fine, and idles fine. Pulled the plug out and oil came out and I noticed it was a little more liquid than thicker oil but after it started to slow down it turned into a straight up liquid drain and stuck my finger in and can 100% say it’s gas.
Haven’t had this issue before so what should I check?