I am making a thin sheet cake, and instead of toring it I was thinking i would inject filling using a piping bag. What is the best way to do this?TIA

Ive always wondered that myself...Ive thought of doing it, and then said...no my cake will bulge...any ideas?

i was almost going to use my cup cake filler tip....

Ive done something similar for my kidz when they were little - except I used pudding or jello. Pokes holes all over with end of wooden spoon or skewer then poured the pudding or jello on top and smoothed out. Refrigerated for awhile then frosted ..
Kinda the same .. HTH Gaye

I often do this for sheet or other smallish cakes.
I fill a pastry bag w/any filling that is smooth (so as not to plug up the tip) and use a tip 3 or 4. Push the tip into the cake and give a fairly good squeeze. That's all there is to it. If the cake is like a sheet...12x8 or bigger, do this about every 2-3" depending on how much filling you want.