I’ve read the linked article. There is no explanation for where the nearly 800 children for whom there is a record of death were buried.
Your reading comprehension is lacking. There was a small plot in the back of the property where they were buried. And there is no proof that where the 20 or so bodies were found was ever a septic tank. It was likely a common crypt for stillborns.
But don’t let that stop you from siding with the liberals/progressives in Ireland trying to use this false narrative to push to legalize more “humane” treatment of babies, i.e., legalized abortion. Amazing how much anti-Catholic liberals and progressives make common cause with anti-Catholic fundamentalists. A lot like progressives make common cause with radical Islam.