Bookmaker Tom Waterhouse has been told to draw a line between his business and that of his mother, leading racehorse trainer Gai Waterhouse.

Racing NSW chief steward Ray Murrihy told the More Joyous inquiry there was nothing to suggest Tom Waterhouse had passed on any inside knowledge regarding the condition of the mare before she ran second last in the All Aged Stakes on April 27.

All betting records pertaining to the race, including those of Waterhouse were scrutinised and nothing untoward was found.

However, Murrihy told the bookmaker to be careful with his family association when advertising his business.

"There is a line between your role as a bookmaker and your mother's role," Murrihy said.

"You need to take care in your advertising.

"Some of it gets too close to the bone.

"You need to isolate what you are doing from what your mother does.

"We don't want to see these types of allegations being aired so publicly again.

"Be mindful of public perception.

"Your business is your business, her business is her business."

John Singleton, owner of More Joyous, sparked the inquiry when he publicly sacked Gai Waterhouse as his trainer after the mare's All Aged Stakes failure and accused her son of inside knowledge there was something wrong with the horse.