Athought it seems very homo, sticking something in your butt can be very horny.
First use the showerhead to clean up your anus. Sit on the toilet and press the showerhead against your hole, while the warm water is cleaning up your inside.
After your ass is clean and all streched up. Now put a carrot or anything like that in your butt. Using your left hand to press it in and out. And using your right hand to masturbate normally, you will get an fantastic orgasme.
Don't let anyone caught you in act! But I'm sure once you find out how great it feels, you will do it more often.