I dont understand Singed. Ive never had any trouble at all against him.
There is no reason for Yorick to get within melee range of Singed. He has W and E which he can spam and crank out tons of ghouls. This will wear Singed down very quickly. Why would you want to get in range of Singed, get tossed into poison for? Just to use a Q? That seems really dumb.
In theory singed can poison creeps, but early on his poison just doesn't do all that much damage, and he doesn't have the sustain to eat W,E after W,E... he eventually has to retreat and heal.
You run in with gas on, gas everything. If Yorick hangs around to Q you, you fling and slow him, then run to his side of the lane and take his health pack (assuming top health is already used). If he chases to the tower, he gets gassed. You run back to where he's at and fling him into your poison again, then go back to pushing. You will push faster than him.
Once you get your ult, you basically become immune to his harass, troll with ult, push minions while threatening him with flings and force him to camp his tower.