i dont worry about regular gas so much as the mixture stuff. if you let that sit especially in a very small engine like a chainsaw or leaf blower, it can really screw things up. but in any case, id say why not drain/refill every 6 months? if you’re just gonna dump it in your truck then why not? not like you’re just throwing away 5 gallons of gas, and its cheap insurance that way too. better safe than sorry