https://www.techpowerup.com/263317/ek-releases-pumpless-versions-of-ek-quantum-reservoirs
 
EK, the premium liquid cooling gear manufacturer based in Europe, is releasing pumpless versions of the Quantum Line pump-reservoir combo units - the EK-Quantum Kinetic FLT D5/DDC Body D-RGB and the EK-Quantum Kinetic TBE 200 D5 Body D-RGB. This means the customer can attach his already owned DDC or D5 pump allowing for a more affordable upgrade process from the previous generation of reservoirs. EK-Quantum products come with sophisticated 5 V D-RGB addressable LEDs which can be controlled through your motherboard RGB control software.

These models are pumpless versions of the EK-Quantum Kinetic FLT pump-reservoir combos. They come in three sizes, 120 mm, 240 mm, and 360 mm. They are mounted from the backside using the 120 mm fan mounting holes and due to having no pump at the back. Each is compatible with both the D5 and DDC pumps and they come with separate mounting kits for your pump of choice, so if you decide to switch the pump model in the future, you can do that without replacing this combo unit.
 
I like the fact that if you already own a DDC or D5 pump you can have purchase this and it  can save you some cash. 
 
 
 


 

They would also look good mounted external of the case
 
I agree this is not a cheap option ... just the "new thing" in custom loops lately ... airflow is always a concern to address in your plan