Three members of the Spence family, Ulster rugby player Nevin, 22, his brother Graham, 30, and their father Noel, 58, died in the tragic accident at the family farm in Hillsborough on 15 September last year.
At an inquest into their deaths on Monday, it was revealed that Graham climbed into the slurry pit first, after being alerted by his father Noel that their collie dog had fallen in.
The slurry tank was under a shed housing cattle. At around ten foot deep, it had contained around three and a half feet of slurry at the time.
Graham climbed down into the tank and had a quick look for the animal. A family friend, who was working on the farm, told the inquest Graham began to climb the ladder when he passed out and fell into the tank.
After seeing his brother fall, Nevin followed him into the tank while the family friend went to get help.
Their father Noel then went into the tank.
Noel managed to get his son Graham up the ladder before he also was overcome by fumes and they both fell back into the pit, the inquest heard.
Senior Coroner John Leckey heard neighbours describe how they tried in vain to rescue them.
I found Graham, I pulled him up by the waist of his jeans. But suddenly I felt faint and sleepy.
Emma Rice, Noel's daughter, also told the coroner how people tried to move her away from the slurry pit opening.
But despite the danger, she went in, dragged her father up the ladder with the help of her neighbours and tried to resuscitate him before going back in to try and rescue her brothers.
The young artist was taken to Belfast's Royal Victoria Hospital for treatment for the inhalation of fumes as she too was overcome by the poisonous gas coming from the pit and had to be rescued by neighbours.
Nevin was eventually recovered from the pit by fire and rescue service crew wearing breathing apparatus.
Noel and Nevin died at the scene, while Graham died a short time later at Lagan Valley Hospital.
When questioned over the dangers of being around the slurry pit, Emma told the coroner: "When it comes to the love of your family, it doesn't matter."
Mr Leckey said her actions were "extremely brave".
The court was told the slurry emitted a number of harmful gases including hydrogen sulfide, carbon monoxide, methane and ammonia.
Mr Leckey said he was concerned at the number of recent deaths in slurry accidents and said it was a "serious problem".
Mrs Rice's sister Laura and mother Essie were in court for the first day of evidence.
The inquest continues.