It does not get you higher than IVing, since the bioavailability of IV is 1% higher than rectal (IV = 100%, rectal = 99% ) and the onset is a bit slower, however it is a safer ROA, than IVing by FAR and many former IV users of various drugs choose to plug it instead, myself included, although I have personally never plugged heroin, however I have plugged morphine, oxy and hydrocodone, crystal meth/desoxyn, adderall/dexedrine, MDMA, cocaine, and a few others, and it is definitely the best ROA for most drugs, seeing as it has essentially the same bioavailability as IV yet it is less immediately dangerous to the body than almost any other ROA aside from oral. It will not give as intense a rush as IV or smoking, but it's long-lasting and healthier. I recommend you switch from IV to plugging wholeheartedly, save yourself the possibility of some serious bodily harm.
Use as small a syringe as possible (no needle, obviously), prepare the exact same size shot as you would usually do, lube up the syringe, stick it up your behind, and pull the plunger. Make sure the syringe is at least 4 inches in.