Have had three other dogs in my life and never encountered this issue. 18 week old female sato mix puppy. She will pee outside but only poops inside when we’re not looking. She’s taken out on a leash in the backyard and we’ve tried staying out there for 15 minutes at a time return inside then immediately take her back out and nothing. 10-15 mins later we find poop in the house. Any help?

Take her for a walk before feeding her breakfast.

18 minutes ago, li_bass_hunter said:

She’s taken out on a leash in the backyard and we’ve tried staying out there for 15 minutes at a time return inside then immediately take her back out and nothing. 10-15 mins later we find poop in the house

Unfortunately you have accidentally trained her to poop in the house.  Now you have to wait her out.  You are going to have to stay outside with her until she can't hold it anymore.  @roadwarrior has given you excellent advice to walk her legs off.  Walk her until she poops and then praise her like she just saved your life.  If you "food train" your dogs (I don't and I don't encourage that) then the first couple times she poops outside an immediate treat would be in order.  I also suggest that you make a code phrase for going to the bathroom, such as "go potty" or I use "take a break".  When you take her out the very second she starts to pee or poop start repeating your code phrase.  Pretty soon you can take her outside and get her to go on command.  She's a beautiful dog!

 

16 minutes ago, BigAngus752 said:

Unfortunately you have accidentally trained her to poop in the house.  Now you have to wait her out.  You are going to have to stay outside with her until she can't hold it anymore.  @roadwarrior has given you excellent advice to walk her legs off.  Walk her until she poops and then praise her like she just saved your life.  If you "food train" your dogs (I don't and I don't encourage that) then the first couple times she poops outside an immediate treat would be in order.  I also suggest that you make a code phrase for going to the bathroom, such as "go potty" or I use "take a break".  When you take her out the very second she starts to pee or poop start repeating your code phrase.  Pretty soon you can take her outside and get her to go on command.  She's a beautiful dog!

 

How have I accidentally trained her to poop in the house 

I agree with all of the above advice. If she'll chase a ball or play fetch, that's a great way to make her run. Almost every time I play fetch with my bassett hound, she stops and poops?.

 

She's a pretty girl!

We’ve only had her for a few days. Guess I got lucky with my other pups they caught on quick when they were young 

Your solution is call umbilical cord training.

Umbilical Cord Training is a housebreaking method that’s pretty much what it sounds like – your dog is attached to you with a cord (his leash) throughout the day. It’s a supervision-based program that requires vigilance but yields excellent results with just about every dog or puppy. This method works well in conjunction with other methods, such as crate training.

Here's more info ~ https://thehousebreakingbible.com/training-umbilical-cord-training/

 

https://www.martindaleanimalclinic.com/userfiles/Umbilical-Cord-Housebreaking-Method.pdf

 

 

Good Luck 

A-Jay

9 hours ago, li_bass_hunter said:

She’s taken out on a leash in the backyard and we’ve tried staying out there for 15 minutes at a time

Unless it's not practical for some reason, the easiest solution is to walk your dog, and not just once around the block. There are a number of upsides to this, but for your immediate purposes you'll probably encounter spots that other dogs use to defecate. The scent left behind will trigger your dog to do the same. If the issue persists, then get a crate. Dogs, especially females, will rarely release where they sleep. At the same time every day, which is important in the beginning, take her from the crate straight on a walk. Dogs like a routine.