The case mounted by Melbourne stewards against Sydney trainer Con Karakatsanis and his father Tony "stretched credibility" and should be rejected, their lawyer told Victoria's Racing Appeals and Disciplinary Board on Monday.

After a day of legal wrangling in which both sides failed in applications, RAD Board chairman Russell Lewis said he would announce a verdict on Tuesday.

Counsel for the stewards Dr Cliff Pannam, QC, opened proceedings by seeking to alter the charge against the two to reflect the new direction of their argument which alleges the accused men planned to administer a bicarbonate drench to Howmuchdoyouloveme.

In all previous stages of the protracted case, the charge had concerned powder found with a drenching kit in Howmuchdoyouloveme's box that tests showed to be a saline drench.

But the Board rejected that application and delivered the same decision to defence lawyer Terry Tobin's application for all five charges against his client be dismissed.

The case against the pair hinges on the events of the early afternoon of November 3 leading up to Howmuchdoyouloveme's appearance in the Yellowglen Stakes at Flemington.

In a covert operation prompted by a tip-off, stewards discovered a bag containing tubing equipment in a stall occupied by Howmuchdoyouloveme.

It was initially alleged the pair planned to drench the horse with a mixture containing the powder found with the other equipment, which would have been against the rules of racing due to the proximity of the race.

But it was established that such a drench administered before a race would be "madness" and could seriously harm a horse.

Tobin said Dr Pannam, having accepted that point, "radically altered" his case by abandoning an argument that had been shown to be unsustainable and substituting an alternative.

In his closing submission on Monday, Tobin said certain ingredients vital to any kind of drench was "nowhere in sight" when stewards pounced on the father and son only 10 minutes before the deadline for the horse to arrive at the racecourse.

He said there had been no water present and the bicarbonate required if the steward's case was to be accepted, was in another room in the stable complex where the horse was housed.

Tobin also questioned why the tubing gear was still in its bag and not being prepared for use.

Dr Pannam told the RAD Board the case hinged on whether it accepted Tony Karakatsanis' testimony that he carried the bag containing the tubing equipment into Howmuchdoyouloveme's box in the mistaken belief it was a bag of hay.