Opioids Issue with rectal administraion of opiates

Hey There, sensitive topic but I thought the community here could help with an issue.

I am new to rectal administration of opiates, mostly hydrocodone and has ran into an issue when trying to push the liquid drug into the rectum via an oral syringe.

I has found that the plunger (The thing you press down on) is extremely hard to press at first and while attempting to push the drug up his rectum.

He has tried three different types of needless syringes, has tried lube and no lube, has tried a full syringe and a half full syringe and I always have an issue pressing the plunger down. I has also tried different positions as well. Laying on his side, missionary, just bending over, ect.

I am a bit overweight which he knows does not help, but can anyone give him some tips so the plunger may not be so hard to press. I ultimately loses some of the drug because he has to pull it out of his rectum a bit so he can get enough force to get the plunger pushed. This causes the syringe to not be as far up his rectum as it should be.

I knows this is a weird topic, but he asks for your maturity and help as he is stumped in regards to ideas.