Pump Flow

[MickR33]

Hey i have a problem with my setup, i have a main resivor and tgat connects to 2 other tubs, i have a pump in the resivor which has a 19mm hose going to the first tub and then continuing to the second tub which has an elbow pointed down and a short piece of pipe going down into the tub, the first tub has a t piece with a short pipe going down into the tub as well so its like this

res>------|-------------|
t piece -> | elbow -> |

the problem is the pump only gets water flowing into the first tub and doesnt make it to the secong tub, i wanted this so i can circulate water from the resivor to both tubs but its not working how i thought, my thoughts are that it is because the t piece is pointing down so gravity and lack of pressure stops it from making it to the second tub.
What are your thoughts on this and what could i do to fix it, i dont think i would want to have it circulating too fast so that means i wouldnt want more water pressure, maybe if i pointed the t piece upwards and then bend the pipe down?
Please help