The toilet and shower in the main bathroom are draining slow. Can I use canned compressed air to clean trap.?

I was at Home Depot one day, in the plumbing section, and saw the canned air. Store worker told me it might work, but I would need to cover up the overflows, so as to not lose the air. Has anybody used this compressed air technique? Also, today is SUNDAY, and you know what that means 'rate wise'!.... show more I was at Home Depot one day, in the plumbing section, and saw the canned air. Store worker told me it might work, but I would need to cover up the overflows, so as to not lose the air.
Has anybody used this compressed air technique?
Also, today is SUNDAY, and you know what that means 'rate wise'!. Suggestions on how to get by until tomorrow?

Thanx,

Dick
Update: Clarification. By 'rate wise' I mean week end fee schedule. Xpensive. Poor me right? Probably soon to be!
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