Tummy tuck wound: Tiny hole with an open "tunnel" next to it, pus under skin; Cleaning inside with saline with a syringe myself?

It's common to have an open area after a tummy tuck and dressing changes can help with healing.  Make sure your plastic surgeon is following you closely.

are best managed by your surgeon.  Your surgeon's experience and wisdom learned through the years will help you have a happy ending.  Make sure your surgeon is aware of any changes for the worse or if you are developing more and more concerns as it is his/her job and obligation to help you through this journey.

It seems as though your surgeon is keeping a close eye on the situation.  The best advice I believe anyone can give you is to continue with this close follow-up - only in person can one accurately diagnose what is happening and then offer you good advice.  These type of wound issues, while a nuisance, typically heal without problem.