Unfortunately the best I can do is explain briefly myself. So basically the allantois/urachus is the structure where the fetal urine will flow through to the umbilical cord.
After birth, if there is a patent urachus, then there ends up being urine dribbling out of the umbilicus because it is actually attached to the bladder and thus there is a direct line between the bladder and external environment, with no sphincter regulation of flow.
Another thing you should be familiar with is the vitelline duct. The VD connects the umbilical cord to the midgut, and if it doesn't completely regress then you may end up with the infamous Meckel's diverticulum, which is also known as an ileal diverticulum. Now, if the entire VD is patent, you can end up with a ileal fistula, where you can get defecation out of the umbilicus in a baby. Similar concept with the allantois/urachus, except now you have a direct line from the ileum to the external environment.
I know this might not be very detailed but it's what I know about it. Hope it helps
