My gf and I have added a strap-on and King Cock 8" dildo with a girth of 6" to our collection of adult toys. We both enjoy anal play so it seemed the ideal choice allowing my partner and I to both participate in the fun simultaneously. I have played with buttplugs etc for years and girth has never been the issue, however, the length of our 8" friend is. The other night my girl got really into the swing of things and really went for it, delivering the full 8" deep inside of me at which point I felt a dull pain which I now know to be the dildo meeting the rectosigmoid junction. No long term damage done and I felt fine once she withdrew but I want to know if there is a means of training yourself to take the full length without experiencing the dull pain as I know she would love to thrust her new toy deep inside me as and when she chooses? There are many videos on adult sites of couples using much longer dildos without issue. Interested to hear your thoughts.
It’s a natural stretch process and needs gradual pressure to flex the inner wall, not an over enthusiastic battering ram that could cause long term damage. Go easy, relax and be sympathetic to each other
It’s all about training and practice I’d guess. The more you try it out the less discomfort you’ll feel
We have an 8" Lifelike Lover dildo for pegging. It has a very gentle taper from 4" girth at the tip to 6" at the base so it slips in very easily but gives a nice stretch when fully inserted. This may help you to get used to the 8" length gradually.
Welcome to the forums 
As said above.
I’ve been considering getting a more flexible and longer dildo that I could use to try and work on that myself. We have a 7.5” dildo that I can’t take all the way because of the same thing.
We have just purchased an XL lubricant applicator syringe and good quality anal silicone lube. Hopefully some well placed lube both in the anal cavity and at the rectosigmoid junction will enable the dildo to glide by the wall allowing pain free full penetration with our strap-on. Fingers crossed.
It is all about training and being completely relaxed.
A great way to train to take a dildo deeper is to start with a flexible double headed dildo and practice to by yourself to get it deeper inside.
it will be a bit difficult but when you find the right position, for instance on you left side with your right leg pulled up.
you can really feel the dildo slowly go around the bend and then you can push the dildo deeper.
When it is getting easier each time you can increase the diameter till you reach the diameter of the strapon. Then you will experience you can take the full length without any discomfort or pain.
Try using the toy in your hand or partners hands and slowly work it in after several sessions it will get easier, it can help if you push out whilst she works it in, a while back my wife was doing me with our very large toy and at one point i felt it pass through the upper ring felt nice once through.